1. Field of the Invention
The present invention relates to pneumatic accelerator apparatus for processing particulate matter, and specifically relates to a pneumatic accelerator structured to provide controlled acceleration of bulk materials to enable the particles to be selectively dispersed, isolated, stratified, electrified and classified which further enables select conveyance, drying, mixing, classification, crushing and micro-pulverization of such bulk materials.
2. Statement of the Art
Devices configured for entrainment of liquids and/or solids via high volume gas or liquid flow into and through a conduit are known in the art and are used extensively in a wide variety of industries, such as mining, milling and agriculture, and include structural applications ranging from pneumatic materials conveyors to dredging nozzles and air cannons. A structural application particularly relevant to the present invention is dilute phase pneumatic conveyors, which are so named in the industry because they employ solids-to-gas weight ratios below ten.
Typical dilute phase pneumatic conveying devices are described in U.S. Pat. No. 3,602,552 to Morgan, U.S. Pat. No. 3,975,058 to York, U.S. Pat. No. 4,711,607 to Wynosky, et al., U.S. Pat. No. 5,718,539 to Segota and U.S. Pat. No. 5,863,155 to Segota. Such conveying devices are typically comprised of a motor-driven screw or auger conveyor mounted within a tube or barrel and a gravity-fed hopper for supplying particulate material to the auger conveyor through an opening in the barrel. This conventional arrangement is capable of establishing a high velocity air-flow where material ejected by the screw conveyor is subjected to one or more jets of pressurized air. The mixture of material and gas thus formed is propelled by the pressurized gas through a conduit connected to a mixing chamber. Such devices typically require a high volume, relatively low pressure gas supply-employing working pressures of up to 15 psig, as measured at the gas source, to create gas flow conditions sufficient to entrain and convey materials.
Conventional suction dredging, vacuum, and air cannon apparatus, such as that described in U.S. Pat. No. 4,776,731, typically utilize high pressure, low volume air or liquid flow produced by a compressor or high pressure pump to produce vacuum pressure in a conduit. The low volume, high pressure gas or liquid is introduced into a combined intake and conduit via a venturi-like device, such as a nozzle or jet, which is integrally connected with an intake conduit and positioned at an angle so that the flow is directed toward the exhaust end of the conduit, thereby potentially creating a substantial vacuum wherein various substances may be entrained at the intake end and conveyed through the conduit to an exhaust end. Vacuum and air cannon apparatus typically are able to produce supersonic gas flows through the venturis or jets to assist in creation of the suction required to entrain materials, sometimes with vacuum pressures of up to 12 inches of mercury. To establish and maintain this type of gas flow, such integrated systems typically require between 90 to 150 psi working pressures measured at the gas source.
Of particular interest when considering conventional dilute phase pneumatic conveying devices, like the devices described in U.S. Pat. Nos. 3,602,552; 3,975,058; 4,711,607 and U.S. Pat. No. 4,776,731 to Briggs, et al., is the nature of the nozzle that is used to accelerate the air. That is, they all disclose a nozzle with an inner linear contour and a nozzle or venturi configuration which is of the convergent divergent type, meaning that the end of the nozzle converges to a point of transition with a conduit and the conduit is structured with a divergent opening. The convergent/divergent configuration of the nozzle in such devices, coupled with the means for producing gas flow within the device, produces conveyance of materials in typically a rotational flow.
Problems exist with conventional types of dilute phase pneumatic conveyance systems, most of which relate to excessive wear in the apparatus due to the design of the apparatus and due to the ineffectiveness or inefficiencies of the devices. For example, two main types of premature wear are found in conventional pneumatic conveyance devices, namely wear within the feed mechanism (e.g., the auger or screw conveyor and associated components) and wear within the conduit itself. Excessive wear in conventional conveyor apparatus is a natural by-product of materials processing and results in increased costs associated with maintenance of the apparatus due to wear and nonproductive downtime associated with replacement of worn parts. The components affected by wear include the inner feed hopper walls, the screw conveyor and shaft, the shaft seals and bearings, the inner wall of the barrel and areas of the mixing zone.
Wear within the conduit is due to the flow pattern of the accelerated air used to entrain the material in conventional devices. That is, vortical (i.e., rotational) flow patterns are conventionally believed to represent the most efficient conditions for the introduction and entrainment of materials. However, problems occur when centrifugal force acting on the particles entrained within the fluid travel in a circular or helical path. Specifically, centrifugal force can cause larger particles to strike the inner surface of the conduit, thus causing premature wear. Conversely, centrifugal force on smaller particles is not significant and smaller particles travel through the apex of the vortex. But the apex of the vortex is not stable and provides another source of wear because the apex continually changes position as it seeks to find a reference point within the conduit, thus directing material to contact the conduit walls. Further, if an increase in head pressure inside the conduit occurs, usually as a result of increased material saturation or of conduit length, in time the unstable vortex will become inverted. Prolonged time in the inverted state invariably causes the vortex to collapse, resulting in inefficient and inconsistent material feed into the gas stream and potential conduit blockage.
Wynosky and Mraz describe such a vortex-creating apparatus in their previously identified patent. The patented apparatus is substantially comprised of a plenum with a single tangentially aligned gas inlet to introduce pressurized gas to a venturi nozzle, which accelerates the gas flow sufficiently to establish a vortex in the mixing chamber zone of the apparatus. Material is then metered and injected via a screw conveyor feed to the vortex and into the conduit. The tangential positioning of the inlet relative to the plenum dictates the creation of vortical flow out the end of the venturi nozzle with a specific orientation of rotation that cannot be modified.
Blowback is another common problem observed in prior art devices and is created when the level of material entrained within the gas stream and/or the length of conduit causes the pressure in the conduit to exceed a critical level. When the pressure is exceeded, some of the accelerated gas and entrained material are forced to flow back through the feed tube or barrel and out the material feed hopper, thus preventing material feed into the gas stream. As a result, there is a loss of gas flow through the conduit and a corresponding loss in velocity which can cause the conveyed material to drop out of the air-stream and buildup in or plug the inside of the conduit. Blowback can also cause severe dust problems and/or contamination of the materials being processed. Typical solutions to blowback include incorporating mechanical flaps near the barrel opening, tapering the barrel or otherwise modifying the auger conveyor flight to produce a material plug in the end of the conduit, or controlling the material feed via the auger conveyor motor speed to regulate material-to-gas ratios, thereby preventing over-saturation of the material flowing through the product conveying line. Such solutions do not guarantee prevention of blowback, however, because the solutions do not address the fundamental issue of gas flow as a contributing factor to blowback.
Conventional pneumatic conveyance devices are not designed to effectively control or modify the gas flow pattern moving through the system and are, therefore, unable to control the vorticity of the materials and gas moving through the system. As a result, the conveyance device is subjected to premature wear. Further, because conventional conveyance devices cannot effectively control gas flow patterns, conventional devices are not known to be capable of providing anything other than conveyance of materials from one point to another. Such devices are not know to be able to dry, pulverize, sort or classify the materials being conveyed. Another problem exhibited with the conventional devices, such as that disclosed in the Wynosky, et al. patent, is the difficulty in introducing material into the feed hopper in other than a nearly horizontal position, effectively limiting the use of the device to those applications which first transport material horizontally and, perhaps, vertically after the material is accelerated.
Thus, it would be beneficial in the art to provide a high volume, low pressure dilute phase accelerator apparatus in which the gas flow pattern of the device is capable of being controlled and modified to selectively produce multi-phase flow patterns through the device to prevent premature wear in the system, to selectively disperse, isolate, stratify, electrify and classify the particles being conveyed and to facilitate not only conveyance, but drying, pulverization, sorting, classifying and other materials processing. It would also be beneficial to provide a pneumatic conveyor apparatus which is structured to effectively prevent blowback and one which can be mounted or operated in any orientation (e.g., vertically, horizontally or on an angle) to accommodate the widest variety of applications.